The invention relates to separation of luminance (Y) and chrominance (C) in a TV composite signal, particularly to Y/C separation for a TV composite signal using a comb filter bank.
A typical color TV decoder receives a composite TV signal as input. Using a comb filter, the color decoder separates Luminance (Y) and Chrominance (C) from the input signal. Next, the comb filter applies the band-pass filtering for the C signal and the band-stop filtering for the Y signal. Thirdly, the C signal is de-modulated back to the base-band region. Fourthly, a low-pass filter band-limits both the de-modulated C signal and the Y signal. Lastly, the band-limited Y and C signals are converted to Red, Green, and Blue outputs.
The composite signal allocates Y and C in the three-dimensional spectral positions in a three-dimensional spectral space. When represented in a one-dimensional or a two-dimensional subspace of the three-dimensional spectral space, the spectrum of Y and C overlap with each other. As such, one-dimensional and two-dimensional comb filters cannot separate Y and C completely. Rather, only three-dimensional comb filters can separate Y and C from a digitized composite image sequence completely. Moreover, as a genuine nonlinear characteristic of an image, edges inside image make difficult any Y/C comb filtering for completely separating Y from C or C from Y in a composite TV signal. Even worse, in an image sequence or video, motions inside image exist in a speed to any directions. Therefore, without perfect motion estimation for the motion of edges in addition to the motion of an ordinary object, the complete Y/C separation cannot be achieved by a one-dimensional or two-dimensional linear comb filter.
However, few real three-dimensional Y/C comb filters are available for a digital color decoder. Even a conventional three-dimensional comb filter operates mostly for the condition of motionless image sequences. It does not fully take advantage of the strong points of three-dimensional comb filters.
For example, most of video signal includes lots of motion contents, but a conventional three-dimensional comb filter function merely two-dimensional comb filter in the spatial domain. Specifically, conventional three-dimensional comb filters simply apply to the conditions of motionless parts in video by a go-no-go decision, wherein the temporal filter function of these three-dimensional filters is not selected in most case. Therefore, a conventional three-dimensional comb filter typically operates merely as a two-dimensional comb filter. For that reason, the conventional three-dimensional comb filter is ineffective when filtering complex motion video content. As another example, memory buffers are necessary to store data for performing the temporal filtering of a conventional three-dimensional filter. However, by operating merely as a two-dimensional comb filter most of the time, the conventional three-dimensional filter rarely use these precious memory buffers.
A method for separating luminance (Y) and chrominance (C) of a composite television digital signal is provided. The method includes analyzing said composite signal to search for one of a plurality of pre-defined motions; in response to a pre-defined motion being detected, filtering the spectral energy of said detected pre-defined motion by a one-dimensional temporal comb filter selected from a filer bank; in response to no pre-defined motion being detected, analyzing said signal by searching for an edge in a three-dimensional sample space of said signal, wherein said sample space is spanned by a horizontal axis, a vertical axis and a temporal axis, and wherein said edge represents a motion encoded in said signal; in response to said edge being detected, selecting a filter of said filter bank in accordance with the orientation of said edge to filter the spectral energy of said motion; and in response to no edge being detected, selecting a three-dimensional spatial-temporal comb filter of said filter bank.
A method for separating luminance (Y) and chrominance (C) of a composite TV digital signal is provided. The method includes searching for motion encoded in said signal, wherein a motion is represented as an edge in a three-dimensional sample space of said signal, said sample space spanned by a horizontal axis, a vertical axis and a temporal axis; in response to detecting a first motion that matches one of a plurality of pre-defined motions, select a one-dimensional temporal filter of a filter bank to filter spectral energy corresponding to a first edge that represents said first motion in said sample space; and in response to detecting a second motion that is different from any of said n pre-defined motions, selecting a filter of said filter bank to filter spectral energy corresponding to a second edge, said filter selected according to the orientation of said second edge in said sample space.
A method for separating luminance (Y) and chrominance (C) from a composite TV digital signal is provided. The method includes searching for a plurality of pre-defined motion cases, said plurality of pre-defined motion cases comprises the motionless case; in response to finding at least one of said pre-defined motion cases, performing Y/C separation of said composite TV digital signal by selecting a one-dimensional (1D) temporal comb filter from a filter bank, said filter bank comprises a plurality of 1D temporal comb filters in one-to-one correspondence with said plurality of pre-defined motion cases; in response to finding none of said pre-defined uniform motion cases, performing Y/C separation of said composite TV digital signal by selecting according to a selection method a filter from the portion of said filter bank that comprises a 1D horizontal (H) comb filter, a 1D vertical (V) comb filter, a two-dimensional (2D) horizontal-vertical (HV) comb filter, a 2D horizontal-temporal (HT) comb filter, a 2D vertical-temporal (VT) comb filter, a 3D horizontal-vertical-temporal (HVT) comb filter.
A filter bank for a TV composite signal is provided. The filter bank includes an one-dimensional (1D) temporal comb filter adapted to perform Y/C separation for a motionless image; a plurality of 1D temporal comb filters adapted to perform Y/C separation by limiting spectral energy associated with an image motion detected having a pre-defined uniform velocity; and a plurality of two-dimensional (2D) comb filters. The 2D comb filters include a 2D spatial (HV) comb filter adapted to limit spectral energy along horizontal and vertical frequency axes of a 3D spectral space of said signal; a 2D spatial-temporal (HT) comb filter adapted to limit spectral energy along horizontal and temporal frequency axes of said 3D spectral space, and a 2D spatial-temporal (VT) comb filter adapted to limit spectral energy along vertical and temporal frequency axes of said 3D spectral space. The filter bank includes a three-dimensional (3D) spatial-temporal (HVT) comb filter adapted to limit spectral energy along horizontal, vertical and temporal frequency axes of said 3D spectral space.
A color TV decoder for a TV composite signal is provided. The color decoder includes a motion detection unit adapted to detect any of a plurality of pre-defined velocities from a set of gray level differences; and a filter bank coupled to said motion detection unit. The filter bank includes a one dimensional (1D) temporal comb filter adapted to filter a motionless image detected by said motion detection unit; a first plurality of 1D temporal comb filters adapted to filter an image motion detected by said motion detection unit as having a velocity that is equal to one of the said plurality of pre-defined velocities; a second plurality of 1D comb filters adapted to limit spectral energy along one of the three frequency axes of spectral space; a third plurality of two-dimensional (2D) comb filters adapted to filter an image by limiting spectral energy along two of said three frequency axes; and a three-dimensional (3D) comb filter adapted to filter an image by limiting spectral energy along all of said three frequency axes.
A filter bank for filtering a TV composite signal is provided. The filter bank includes a two-dimensional (2D) spatial horizontal-vertical (HV) comb filter adapted to be activated to filter spectral energy associated with a first edge in a two-dimensional sample space spanned by a horizontal axis and a vertical axis; a 2D spatial-temporal (T) comb filter adapted to be activated to filter spectral energy associated with a horizontal motion, wherein said horizontal motion is represented as a second edge in a two-dimensional sample space spanned by said horizontal axis and a temporal axis; and a 2D spatial-temporal (VT) comb filter adapted to be activated to filter spectral energy associated with a vertical motion, wherein said vertical motion is represented as a third edge in a two-dimensional sample space spanned by said vertical axis and said temporal axis; and a three-dimensional (3D) spatial-temporal (HVT) comb filter adapted to be activated to filter spectral energy associated with a motion that cannot be properly filtered with said above filters.
A filter bank for filtering a TV composite signal is provided. The filter bank includes a first filter set comprising k one-dimensional (1D) temporal comb filters, wherein a filter from said first filter set is adapted to be selected to filter said signal in a first stage of processing said signal, wherein said k greater than 1; a second filter set comprising a 1D horizontal (H) comb filter and a 1D vertical (V) comb filter, wherein a filter from said second filter set is adapted to be selected to filter said signal in a second stage of processing said signal if no filter is selected in said first stage; a third filter set comprising a two-dimensional (2D) horizontal-vertical (HV) comb filter, a 2D horizontal-temporal (HT) comb filter and a 2D vertical-temporal (VT) filter, wherein a filter from said third filter set is adapted to be selected to filter said signal in a third stage of processing said signal if no filter is selected in said second stage; and a fourth filter set comprising a three-dimensional (3D) horizontal-vertical-temporal (HVT) comb filter, wherein said 3D (HVT) comb filter is selected to filter said signal in a fourth stage of processing said signal if no filter is selected in said third stage, and wherein the orientation of an edge in a three-dimensional sample space of said signal is used for filter selection.